Development of stiff shoulder in asymptomatic volunteers during ten-year follow-up in Japan

Objectives: The purpose of this study was to longitudinally evaluate relationships between the incidence of stiff shoulder and sagittal alignments of the cervical spine, age-related changes on magnetic resonance imaging (MRI) and life styles of the subjects. Methods: The subjects were 69 men and 93 women. The mean follow-up period was 11.3 ± 0.7 years. Sagittal alignments of the cervical spine were classified into the following 4 types: lordosis, straight, kyphosis and sigmoid. MRI findings were evaluated for the progression of 1) decrease in signal intensity of disc, 2) posterior disc protrusion, and 3) disc space narrowing. Results: Stiff shoulder was found in 29.6% of the subjects over the 10 years. In the group of subjects 30-49 years old, the incidence of stiff shoulder was 40.4%, and it was higher than those in other age groups. Stiff shoulder was significantly more frequent in women (45.2%) than in men. Its incidence was significantly lower in those who regularly participated in sports or exercise. There were no significant relationship between the incidence of stiff shoulder and the progressions in any of MRI findings during the follow-up period. Conclusions: Stiff shoulder was more frequent in middle-aged, female and non-exercising subjects. There was no correlation between the incidence of stiff shoulder and sagittal alignments of the cervical spine, or progression of age-related changes of the cervical disc on MRI.